1. FIELD OF THE INVENTION
The present invention relates generally to lithographic techniques for microcircuit fabrication and more specifically to a method for forming trenches, vias and holes of sub-half-micron dimensions within microcircuit substrates.
2. DESCRIPTION OF THE RELATED ART
The performance of microelectronic components is greatly enhanced by reducing the size of electronic devices on chips and by reducing the dimensions and spacings of trenches and/or holes imprinted within the substrate. Miniaturization of feature size in the microelectronics industry by the currently used conventional photolithography methods has reached the inherent process limit of .about.0.5 micron. The conventional method for fabricating trenches and/or holes in a substrate is done by photolithography and pattern transfer. The substrate is coated with a UV-sensitive resist film. The resist film is then exposed to a pattern of UV radiation, for example, a parallel grid for trench fabrication. Exposure to the UV pattern alters the resist film structure and reactivity. After developing the UV-exposed resist film, it is dissolved away leaving behind a pattern of the unexposed, unaltered resist film and bare exposed substrate surface sections which were covered by UV-exposed resist film prior to dissolution. Using directional etching, such as reactive ion etching (RIE), perpendicular to the substrate surface, trenches, vias and/or holes with largely vertical walls can be cut into the bare exposed substrate sections unprotected by the etch mask of resist film material. In general, conventional photolithography has an inherent resolution limit of about 0.5 .mu.m for forming trenches or holes. It is almost impossible to achieve a resolution below about 0.4 .mu.m using conventional photolithography.
Additionally, conformal deposition of various metals on the vertical and horizontal surfaces of buttresses attached to the substrate and on the bare exposed horizontal substrate surface sections between buttresses, in the region of sub-half-micron dimensions, has been difficult to achieve. It is also difficult to deposit highly conformal (i.e. of essentially the same thickness, for example, within .+-.2-10% of the average thickness) metal films on the vertical and horizontal surfaces of holes or trenches cut into the substrate in the region of sub-half micron-dimensions. See, Riley et al., Limitation of low-temperature low pressure chemical vapor deposition of SiO.sub.2 for the insulation of high-density multilevel very large scale integrated circuits, J. VAC. SCI. TECIINOL. B 7 (2), Mar/Apr 1989, FIGS. 2 and 3, pp. 230-231, incorporated herein by reference in its entirety; See, Hatanaka et al., H.sub.2 0-TEOS Plasma-CVD Realizing Dielectrics Having a Smooth Surface, VMIC CONFERENCE, June 11-12, TH-0359-0/91/0000-0435 $01.00 C 1991 IEEE, FIGS. 2 and 3, p. 438, incorporated herein by reference in its entirety; See, Lai et al., CVD-Aluminium for Submicron VLSI Metallization, VMIC CONFERENCE, June 11-12, TH-0359-0/91/0000-0089 $01.00 C 1991 IEEE, FIGS. 2 and 3, p. 94, incorporated herein by reference in its entirety; See, Rey et al., Numerical Simulation of CVD Trench Filling Using a Surface Reaction Coefficient Model, VMIC CONFERENCE, June 12-13, TH-0325-1/90/0000-0425 $ 01.00 C 1990 IEEE, FIGS. 3 and 5, p. 426, incorporated herein by reference in its entirety; See, Ahn et al., Advances in Production Methods in VLSI and ULSI Technology Using Isolated-Chamber Sputter Deposition of Al 1% Si Films, VMIC CONFERENCE, June 12-13, TH-0325-0/90/0000-0325 $01.00 C 1990 IEEE, FIGS. 2, 3, 4 and 6, pp. 327-328, incorporated herein by reference in its entirety; See, Raaijmakers et al., Contact Hole Fill with Low Temperature LPCVD TiN, June 12-13, TH-0325-1/90/0000-0219 $01.00 C 1990IEEE, FIG. 1a, p. 222, incorporated herein by reference in its entirety.
For higher pattern resolution holes, vias or trenches, on the order of about 0.25 .mu.m to about 0.5 .mu.m in diameter or width, shorter wavelength mask exposure systems using deep UV or X-ray radiation are needed. Using deep UV lithography, feature sizes between .about.0.25-0.5 microns can be achieved only with difficulty. (See U.S. Pat. No. 4,947,413 Col. 1, Lines 59-60; Col. 2, Lines 36-39; U.S. Pat. No. 5,089,913 Col. 3, Lines 37-39). X-ray photolithography can achieve a resolution below 0.1 .mu.m; however, this method encounters problems in resist sensitivity, source intensity, mask generation and registry. In addition, X-ray photolithography is equipment intensive and expensive.
Thus, a need remains for a lithographic method by which sub-half-micron dimension trenches and/or holes can be produced consistently, inexpensively and with relative ease.